Investigation on the Passivation Behavior of Rebar Embedded in Ecc Contaminated with Chloride Ion

Abstract

Due to the dense microstructure and high resistance to chloride ion erosion, engineered cementitious composite (ECC) possesses of a potential to be applied in the chloride-contaminated environment. However, the passivation mechanism of embedded in ECC with endogenous chloride is still unclear. This study investigates the microstructure of ECC using scanning electron microscopy (SEM) and nitrogen adsorption-desorption (NAD) measurements, while evaluating the passivation behavior of embedded steel via electrochemical workstation testing. The results show that the synergistic effect of fly ash and polyvinyl alcohol (PVA) fiber significantly refines the pore structure of ECC, which is conducive to the early formation of dense matrix. This microstructure effectively impedes harmful ion penetration and preserves structural integrity, even under endogenous chloride exposure. At endogenous chloride levels ≤ 1.25%, steel reinforcement in ECC maintains passivated after 28 days (Ecorr > -126 mV, icorr < 0.1 μA/cm2), which is attributed to the dense microstructure of ECC as an ion barrier. Electrochemical impedance spectroscopy reveals stable passivation film formation in ECC (except at 1.25% chloride), evidenced by small-radius capacitive arcs in Nyquist plots and high-stable phase angles in Bode plots. However, at chloride concentrations > 1.00%, the charge transfer resistance (Rct) decreased sharply while the electric double layer capacitance (CPEdl) increased, signaling rising depassivation risks and behavior. Cyclic polarization curves further confirmed dynamic stability of passivation films at ≤ 1.00% chloride, whereas destabilization and localized pitting tendencies emerged at 1.25% chloride.

Keywords: ECC, Endogenous chloride ion, Microstructure, Electrochemical measurement, Passivation behavior